Torsional Restraints For Downhole Transmissions

ABSTRACT

A noninvasive method for the affixing of a transmission in a downhole housing wherein the housing is deformed, creating an oval cross section, and inserting the transmission into the housing with the greatest cross section of the transmission being positioned along the major axis of the oval created and, thereafter, releasing pressure to cause said housing to return to its normal circular cross section.

The present invention deals, in a general sense, with the mounting of a mechanical downhole transmission within a housing and, in particular, a novel method of transferring torsional loads from the gear train to the transmission housing, to thereby resist twisting of the gear train.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

There are applications in the oil patch in which a mechanical transmission is mounted within a cylindrical housing. Such an application is found when used with a Geared Centrifugal Pump [GCP], such as described in Morrow U.S. Pat. No. 5,960,886. In that application, a speed increasing transmission is linked to a downhole, multistage centrifugal pump and is driven from the surface by a power source driving a rotating drive string.

The transmission is mounted within a cylindrical housing. The discharge from the pump is routed inside the transmission housing via flow tubes, which run along the side of the transmission gear train, as described in Morrow U.S. Pat. No. 8,118,089. The cylindrical housing functions as both the outer gear case for the transmission, as well as a pressure barrier between the high pressure pumped fluid in the flow tubes and the relatively low pressure in the well bore. The inside volume of the housing is kept at pump discharge pressure by a pressure compensator, so there is little to no pressure differential between the pumped fluid flowing inside the flow tubes and the inside of the housing, so as to limit potential leakage of well fluid into the transmission lubricant.

In the case of the GCP, the transmission is required to transmit significant torque between the input shaft of the transmission and the pump. This torque puts large twisting loads on the transmission gear train, which must be restrained so as not to result in deformation of the transmission internal structure and consequent misalignment of bearings, gears, shafts, etc.

The most obvious way to resist this twisting force due to the torque is to tie the transmission structure to the outer housing, which has a fairly thick wall to resist the pressure differential mentioned above and, hence, has great torsional stiffness.

OVERVIEW OF THE PRIOR ART

The current method by which the transmission structure is tied to the outer housing is by means of a series of transverse connecting pins. Specifically, the transmission is inserted into the housing; holes are drilled along its length through the housing wall and into the structural components of the transmission. Two rows of pins are shown in the accompanying drawings at the 12:00 o'clock and 180° away at the 6:00 o'clock positions. Steel pins are then inserted into the holes and into these structural components, leaving a short length of pin engaged within the housing wall. The countersunk hole in the housing is then filled with weld to seal the hole.

This method appears to have functioned satisfactorily so far, but has several drawbacks. For example, a typical transmission using this system will employ as many as 70 pins. Each pin results in a penetration of the pressure housing and, thus, a potential point of failure.

The engagement of the pins in the housing, although small, represents a reduction in wall thickness, which reduces ultimate burst strength of the housing. The process of drilling, pinning and welding is labor intensive and, hence, expensive.

SUMMARY OF THE INVENTION

The present invention teaches a noninvasive alternative to the pinning of the transmission components as described, and, as a principal objective, therefore, offers a novel method of keeping the torsional forces exerted on the transmission from twisting the gear train assembly, causing misalignment and accelerated failure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section through a component of the transmission, showing the prior art pinning technique currently used, as described;

FIGS. 2 a through 2 d show the process of affixing the transmission in the housing in accordance with the teachings of the present invention. Specifically, FIG. 2 a is a cross section of the cylindrical housing; FIG. 2 b shows the housing deformed (ovalized) by the application of lateral pressure; FIG. 2 c shows the transmission inserted into the ovalized housing; and FIG. 2 d shows the transmission held tightly by the housing after the lateral pressure is released;

FIG. 3 shows the texture applied to the contact surfaces of the transmission components, or stand-off spacers;

FIG. 4 shows an axial cross section of a transmission cradle within the cylindrical housing, with stand-off spacers;

FIG. 5 is a side elevation of a cylindrical housing, partially sectioned, to illustrate a typical transmission as it would appear in the housing, once the transmission is inserted and in place;

FIG. 6 is a pictorial representation of a system for the deformation of the casing prior to its accepting the transmission gear train;

FIG. 7 is a side elevation of the system of FIG. 6;

FIG. 8 is a partial cut away of a housing illustrating the interior thereof, with an additional strip in place;

FIG. 9 is a cut away of a partial cross section of the housing of FIG. 8;

FIG. 10 is similar to FIGS. 1 and 4, with the exception that key ways have been cut at zero and 180 degrees in the cradle of the transmission;

FIG. 11 is a cross sectional view of the housing, illustrating placement of the longitudinal strips spot welded, or otherwise affixed, to the interior diameter thereof;

FIG. 12 is similar to FIG. 2B, with the housing compressed and the transmission aligned in the housing such that the key ways cut in the structure of FIG. 10 with the key strips in FIG. 11; and,

FIG. 13 is similar to FIG. 1 in that the housing resumes its circular configuration with the strips situate in the key ways.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference now to the drawings, and initially, to FIG. 1, the current state-of-the-art system is illustrated. The outer housing 10 is illustrated as having a pair of exemplary holes 12 formed along a diameter at the 12 o'clock and 6 o'clock positions, respectively, although the precise position is a matter of common sense choice. The holes 12 are exemplary only, it being understood that as many as 70 such holes may be employed by the current state-of-the-art system. Holes 12 also penetrate the transmission cradle 14 as at 16, and a pin 18 is positioned in each hole 12. In this manner, the transmission gear set is essentially anchored to the outer housing thereby to resist distortion by the application of torque to the gear set by way of the input drive (not illustrated).

Having thus illustrated the current state-of-the-art, move now to FIGS. 2 a through 2 d, which will illustrate, in step form, the novel method by which the shortcomings of the current state-of-the-art may be overcome.

The essence of the present invention is a novel, noninvasive method which takes advantage of the characteristics of such transmissions used in fluid production wells. The present invention has its primary use in production wells configured to draw subterranean fluids to the surface via a production well in which a power source at the surface drives a drill string having a transmission connected with the driving string which, in turn drives a pump immersed in the subsurface fluid. The method of the present intention takes advantage of certain elements of such transmissions are elongated to the extent that they are slightly longer in cross section than the cross section of the housing, or casing, in which the transmission is situate, and, when applied, offers the capacity to hold a speed increasing transmission firmly within a cylindrical housing to resist the reactive twist of the components during high torque operation.

The scientific principle, broadly stated, employs an external force to deform the housing elastically with the external force so that the transmission can be inserted and positioned inside the housing, then squeezing, or compressing, the housing until it becomes oval in cross section, positioning the transmission and releasing the pressure on the housing, which results in frictional engagement with the transmission and thereafter releasing the force to allow the housing to return to its cylindrical shape, clamping the transmission firmly in position. This is the procedure shown in FIGS. 2 a through 2 d.

FIG. 2 a shows a cross section of the cylindrical housing 21, undeformed. FIG. 2 b shows the housing with an external force, represented by arrows 23, applying a radial force exerted toward the center of the cylinder over its entire length.

One such method of applying force is by the use of hydraulic jacks 25 against the casing, or housing, 27 as seen in FIGS. 6 and 7. This application of force in a uniform manner causes the shape of the cylinder to be deformed, going from circular to oval or elliptical, with the principal axis of the ellipse normal to the direction of the force. Note that this internal principal axis is greater in length than the internal diameter of the undeformed housing.

FIG. 2 c shows the transmission 14 inserted into the deformed housing, while the external force is still being exerted. The transmission 14 is inserted into the housing with its largest diameter along the major axis of the oval created by the compression of the housing. The external shape of the components of the transmission is such that the transmission just fits within the deformed housing, and the diameter of some of the transmission components in the direction of the principal ellipse axis is greater than the diameter of the undeformed housing. It is, of course, essential that the deformation does not exceed the elastic limit of the housing material.

Once the transmission is positioned within the deformed housing, the external force is released, and the housing will return to its circular shape, shown in FIG. 2 d. Since many of the transmission components have a greater external diameter than the internal diameter of the undeformed housing, the housing “clamps” tightly on those components and holds the entire assembly firmly within the housing. A cross section of a portion of the transmission held within the housing as described above is shown in FIG. 4.

The bearing surface of the transmission components that contact the inner wall of the housing can be textured, e.g., either by knurling or with machined shallow grooves, 30, that create sharp ridges aligned with the principal axis of the housing, to grip the inside of the housing more securely, as shown in FIG. 3.

It some instances, the components of the device being held do not have sufficient stiffness in those areas where they will be squeezed by the housing after the deforming force is released and may be deformed inward, excessively. In those cases, stand-off spacers which have a larger diameter than the transmission components, can be spaced appropriately to carry the squeezing force of the undeformed housing (FIG. 5). These spacers 31, are located in between the transmission components and pinned, or otherwise connected, to said transmission components, to hold those components fixed during high torque operation, while holding the housing away from these more fragile transmission components.

In summary, in order to accomplish the objectives of the present invention, one must first distort the casing, and that is accomplished by the application of external pressure in a uniform manner and in an amount sufficient to distort the casing without exceeding its elastic limit.

Next, the transmission gearing, supported by its cradles, is inserted into the distorted casing such that the major diameter of the transmission components are situate along the distorted axis of the casing.

Finally, the surfaces of selected transmission components, clearly those components which are stationary, such as the cradles, are roughened such as by knurling, or grooving, such that when external pressure on the casing is released and it returns to its circular cross section, the contact between the knurled, or grooved, surfaces and the inner diameter of the casing provides a rigid connection. In this manner, the objectives of the present invention are achieved.

The present invention contemplates an alternative to the structure previously described. Referring to FIGS. 8 and 9, it will be seen that the housing 10 has been fitted with a longitudinal strip 35, which may be spot welded, as at 37, to the interior wall 39 of the housing and would act as an additional restraint. The strips would be, preferably, spot welded 180 degrees apart to provide additional resistance when the housing is compressed to receive transmission elements.

FIGS. 10 through 13 illustrate the assembly of this alternative structure. FIG. 10 shows key ways 42 cut in the cradle of the transmission at the zero degrees and 180 degrees, the situation being that they are 180 degrees apart. FIG. 11, of course, shows the longitudinal strips 35 as they are affixed in the housing to the interior diameter thereof. In FIG. 12, the arrows illustrate that the housing is compressed to create an oval cross section whereby the transmission itself is readily inserted and positioned within the housing, with the longitudinal strips 35 aligned with the key ways 42. The compressive force is then released, and the resultant structure is illustrated in FIG. 13, with the key ways 42 circumscribing the strips 35 to secure the transmission in accordance with the present invention.

It will be understood that those skilled in the art, may, upon reading of the detailed description, think of various ways to accomplish the invention other than those specifically set forth. It will be appreciated that such variations are within the contemplation of the invention as illustrated by the forthcoming claims. 

1. In a well for the production of subsurface fluids wherein a cylindrical housing, said housing having an interior wall surface and an exterior wall surface, extends from a power source at the surface to a pump immersed in the subsurface fluid; a method of affixing a transmission within the housing, comprising the steps of: applying pressure to compress said housing so as to distort its cross section to an oval configuration; positioning said transmission within said housing at a predetermined level; releasing pressure on said housing so as to permit its return to its circular inside diameter whereby said internal diameter of said housing frictionally engaged with at least a portion of said transmission firmly holding the same in its predetermined position.
 2. In a well for the production of subsurface fluids wherein a cylindrical housing, said housing having an interior wall surface and an exterior wall surface, extends from a power source at the surface to a pump immersed in the subsurface fluid; a method of affixing a transmission within the housing, comprising the steps of: applying pressure to compress said housing so as to distort its cross section to an oval configuration; roughening the surface of the interior diameter of said housing; positioning said transmission within said housing at a predetermined level; releasing pressure on said housing so as to permit its return to its circular inside diameter whereby said internal diameter of said housing frictionally engaged with at least a portion of said transmission firmly holding the same in its predetermined position.
 3. The method of claim 1, comprising the step of introducing hydraulic jacks 180 degrees apart against the exterior surface of said housing and using said jacks to distort said housing.
 4. The method of claim 1, wherein spacers are provided intermittently throughout said transmission.
 5. The method of claim 2, wherein said hydraulic jacks providing a uniform radial pressure to said housing.
 6. The method of claim 1, wherein said interior wall of said housing being textured.
 7. The method of claim 2, wherein said interior wall of said housing being knurled.
 8. The method of claim 1, wherein said interior wall being knurled.
 9. The method of claim 2, wherein said interior wall of said housing being textured. 